1. Field of the Invention
The present invention relates to semiconductor processing and in particular to a method and apparatus for temperature measurement and adjustment of an object using infrared pyrometry.
2. Background of the Related Art
In semiconductor manufacturing, substrate temperature is a critical process parameter. Throughout the various stages of substrate handling and processing, the substrate temperature varies significantly. Measuring the substrate temperature at a given time allows valuable data to be accumulated and analyzed. Feedback can then be used to adjust process parameters or determine the viability of certain process materials.
A preferred temperature measuring device must be reliable and non-intrusive and capable of accurate, reproducible, and process-independent measurements. Additionally, the device must not interfere with the throughput of the processing system, i.e., the productivity of the system. Throughput is related to the idle time during which substrates are not being processed. Therefore, a preferred device does not contribute significantly to the idle time of the system.
A typical non-contact temperature measuring device is a pyrometer capable of detecting radiation from a heated surface. A pyrometer works by measuring the amount of radiation emitted in a certain spectral regime, such as infrared, from the object to be measured. The temperature can then be determined according to known formulas such as Planck's Radiation Law.
Current methods and apparatus using pyrometers are typically capable of in-situ measurement. In-situ systems position the pyrometer with a line-of-sight to the substrate during processing such that the pyrometer receives electromagnetic waves directly from the substrate. Light pipe probes are sometimes used in tandem with a pyrometer to direct the propagating waves to the pyrometer. This allows real-time temperature readings throughout the processing period. Examples of such arrangements are described in U.S. Pat. No. 5,738,440, assigned to International Business Machines, Inc., and U.S. Pat. No. 4,956,538, assigned to Texas Instruments, Inc.
However, in-situ systems are difficult and expensive to implement on existing chambers. For example, deposition chambers equipped with pedestals for supporting the substrates, must be modified to receive optical devices, such as light pipe probes, from the backside of the pedestal. While such modifications are often made for purposes of research and development, it is expensive and impractical for large-scale production.
Additionally, some chambers, such as chemical vapor deposition (CVD) chambers, will not support any form of intrusive optical devices. CVD involves depositing a coating on a substrate by introducing chemical fluids into the chamber and bringing them into contact with the substrate. Intrusive devices, such as light pipe probes, require an "eye," or light inlet, to receive the electromagnetic waves. Over time, the chemical precursors are deposited on the eye and obstruct wave propagation therethrough and prevent accurate temperature measurements.
The disadvantages of in-situ temperature sensing technology has provided impetus for alternative ex-situ systems. In one such system used in processing systems, substrate temperatures are measured in cooldown chambers after processing. The cooldown chambers are fitted with light pipes to receive thermal radiation and determine a substrate temperature. After processing, a transfer robot retrieves the substrate from the process chamber and shuttles it to the cooldown chamber where it is placed on a support member in view of the light pipe. Once a temperature reading is taken, the end-of-process temperature can be determined by extrapolation.
However, such an arrangement suffers not only from the disadvantages involved in retrofitting existing equipment but also from its generation of poor data. During the transfer from the process chamber to the cooldown chamber, heated substrates experience substantial and rapid cooling. The lag between the end-of-process time and the temperature reading in the cooldown chamber leads to increased error in the estimation of the end-of-process temperature by extrapolation.
A number of requirements have limited the flexibility in design changes to temperature measuring devices. In general, the need for high throughput requires the measurement to be simultaneous with other necessary processing events such as annealing or cooling. Additionally, both in-situ and ex-situ systems currently known in the industry require the substrate to be stationary during temperature measurement. As a consequence, temperature measurement devices are commonly located in cooldown chambers or other chambers not involving deposition where substrates reside for a period of time as part of the overall processing sequence. Thus, a preferred device must yield superior data while minimizing detrimental effects on throughput.
Therefore, there remains a need for ex-situ optical detection equipment which is reliable, process-independent, non-invasive, and easily implemented on existing fabrication systems. In addition, the ex-situ device must be able to accumulate accurate data while maximizing productivity.